I tend to think that this King was rejected more because he was good, than for any other reason. Given how selfish Belgium's political class apparently are, it's not surprising they wouldn't like a man who had such strict standards about putting the public welfare first. He was a reproach to them.
It does put me in a bad mood of pessimism. King Leopold III and King Leopold II were very different, Leopold III being a more friendly and humble type, but I think of the complaint often of Leopold II about Belgian attitudes. Both men, and probably all the kings really, unlike all the rest, had a 'national' vision and not one limited by region or their narrow self-interest like the politicians. That is destroying the country we can clearly see. King Leopold III also tried to take advantage of misfortune to serve the national interest. He showed this by staying in the country in the occupation (to serve his people) and by his plan to start a new era in the aftermath. The selfish politicians to the contrary wanted to take advantage of the war misfortune to serve their own ends. That put the country on a dangerous path.
I think they were afraid of the 'new era' the King planned, so they did their best to portray it as something negative, as if he had dictatorial ambitions and so on.